1. Field of the Invention
The present invention relates generally to a semiconductor device having bonding wires, and in particular to the shape of a bonding wire for electrically connecting a semiconductor element and an inner lead portion.
2. Description of the Related Art
In the field of semiconductor devices, it has become important more and more to enhance moisture resistance in accordance with the reduction in the size of the device package and the lead pitch.
In fabricating a semiconductor device which is sealed with resin, bonding wires are used as a means for electrically connecting a semiconductor chip and a lead frame. FIG. 5 shows a conventional bonding wire 1 having a circular cross section. The peripheral surface of the wire 1 is smooth. The wire 1 is made of gold, aluminum alloy, copper alloy, etc.
When a semiconductor device assembled by use of a bonding wire having a cylindrical smooth peripheral surface is molded with sealing resin, adhesion between the mold resin and the lead frame or bonding wire is not satisfactory. When the molded semiconductor device is subjected to an environmental test or it is actually used, moisture enters through a gap between the mold resin and the lead frame and then through a gap between the resin and the bonding wire, thus reaching the semiconductor element. As a result, there is a concern that the semiconductor element may be corroded and the characteristics of the element may be deteriorated. Under this situation, various techniques of preventing the entering of moisture have been proposed, in which the shape of a lead frame is improved. However, the bonding wire has not been improved at all.